Flow cytometry is an analytical technique used in a number of applications to measure physical and/or chemical properties of biological or non-biological particles as they flow in a sample fluid through an investigation cell. Flow through the cell may be investigated by a variety of techniques, including subjecting the flow to electrical, acoustic and/or optical signals and measuring and analyzing responses to detect and evaluate particles in the sample.
Flow cytometers have found wide use in analyzing biological particles having a size on the order of bacteria or cells, typically in a range of 1 to 15 microns in size. However, accurate flow cytometry evaluation of virus particles presents particular problems because of the very small size of virus particles, which typically have a size on the order of tens to hundreds of nanometers.
One approach that has been proposed for flow cytometry evaluation for virus particles is the use of flow cytometers operated at extremely low sample flow rates on the order of 5000 nanoliters per minute or smaller and with continuous monitoring and control of sample flow rate. This approach has been effective to a significant extent, but it is still difficult to accurately and quickly evaluate the extremely small virus particles relative to other biological material components and to accurately control the flow of samples containing a mixture of different biological material components.